Nonlinear optical point light sources through field enhancement at metallic nanocones

Abstract

A stable nonlinear optical point light source is investigated, based on field enhancement at individual, pointed gold nanocones with sub-wavelength dimensions. Exciting these cones with near-infrared, focused radially polarized femtosecond beams allows for tip-emission at the second harmonic wavelength (second harmonic generation, SHG) in the visible range. In fact, gold nanocones with ultra-sharp tips possess interesting nonlinear optical (NLO) properties for SHG and two-photon photoluminescence (TPPL) emission, due to the enhanced electric field confinement at the tip apex combined with centrosymmetry breaking. Using two complementary optical setups for bottom or top illumination a sharp tip SHG emission is discriminated from the broad TPPL background continuum. Moreover, comparing the experiments with theoretical calculations manifests that these NLO signatures originate either from the tip apex or the base edge of the nanocones, clearly depending on the cone size, the surrounding medium, and illumination conditions. Finally, it is demonstrated that the tip-emitted signal vanishes when switching from radial to azimuthal polarization.

Nonlinear imaging of nanostructures using beams with binary phase modulation

“…Due to the unique local polarization distributions of such beams, they give rise to very special 3D field distributions when tightly focused [5,14,15]. For instance, radial and azimuthal polarizations can be used to unambiguously excite oriented molecules and nanostructures [16][17][18][19][20][21][22][23][24][25][26]. Even though the creation of such beams is now well established [10][11][12], their shaping in space and time often involves cumbersome optical setups [25,27].…”

Enhancing light absorption in organic semiconductor thin films by one-dimensional gold nanowire gratings

“…For investigating the optical properties of the grating and hybrid system the sample is illuminated in an inverted microscope (Nikon Eclipse Ti-U) by a white light beam (100 W halogen lamp) that is collimated to within ±3 • , while the transmitted light is detected through a 20× objective. By inserting a pinhole of 200 µm diameter in the image plane of the microscope, light is spatially filtered [41]. Only light which passes the pinhole is detected by the spectrometer, such that specific areas of about 10 µm diameter on the sample can be optically analyzed.…”

Second harmonic generation enhancement by polarization-matched nanostructures -INVITED

“…In the interaction of light with nanostructures many intricate effects can be observed. For light with high local intensities also nonlinear effects, such as second harmonic generation (SHG), can be observed [1,2]. In plasmonic nanostructures, which are most often created from gold, silver or aluminium, collective oscillations of the free electron density (so-called localized surface plasmon polaritons) are excited, leading to high scattering and absorption cross-sections, a high local concentration of optical energy near the nanostructures, strong electric near-fields, and resonances that depend on the geometry, material, arrangement, and dielectric environment [3,4].…”